The mandate of the United States Federal Communications Commission for manufacturers to move swiftly to High Definition Television (HDTV) broadcasting has met with only a tepid response. To date the availability of HDTV signals is very limited and the cost of HDTV receivers is still above the ability of much of the market to afford. To address this need for lower cost reception of HDTV signals, a related invention contained in U.S. patent application Ser. No. 09/714,723, filed Nov. 15, 2000, by George Nickel, teaches a method of transmitting HDTV digital signals with a NTSC analog format. This method can also be used with other conventional analog formats, such as PAL and SECAM. This allows viewing of a digital format on a conventional analog television set.
However, the picture on a conventional analog set has letterbox lines, or blackish lines above and below the 16×9 image, each letterbox line being ⅛ of the full height of the 4×3 screen. In the radio-frequency (RF) broadcast of the video signal, the letter box region can be used to contain information, like high-definition image digital data, or even data unrelated to the video image. Practical algorithms for inserting digital data into the conventional analog broadcast which have high data capacity likely may cause the letter-box lines to contain sparkle or some other time-varying structure instead of being completely black. These time-varying structures likely will be unacceptable to many television viewers. The present invention provides apparatus for intercepting the hybrid HDTV signal before it reaches the conventional television set and insure that the letter-box lines are totally black, without in any way disturbing the HDTV 16×9 image.
It is therefore an object of the present invention to provide apparatus for blackening letter-box lines in HDTV/conventional-analog hybrid systems.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.